Gear



insana retratar clasica@ NIKOLA .TRiaoJEvIcm or DETROIT, MICHIGAN.

GEAR.

Application filed January 3, 1922. Serial No. 526,510.

To all whom it may concern) Be it known that I, N rKoLA TRBQJEVICH, a subject of the King 'of Yugoslavia, residing at Detroit, in the county of Wayne and State of Michigan, have invented certain new and useful Improvements in Gears, of which the following. is a speci'cat-ion, reference being drawings. f

The invention relates to spiral bevel gears and has for its object the obtaining of a construction which can be successfully manufactured by a hobbingfprocess. The process -employed in hobbing, as well as the construction of the hob which is used, are also inventions of mine, but the present application refers solely to the product or gear.

In the' drawings:

Figures l to 3 are the diagrammatic views illustrating the geometrical principles in volved;

Figure 4 shows a side elevation of the gear and hob illustrating the method of generation;

Figure 5 is a plan view of the same;

Figure 6 shows a portion of a gear of the extended type in sectional perspective;

Figure 7 is a sectional plan view of a crown gear and pinion ofthe abridged type;

Figure 8 is a similar view of the improved gear meshing with a taper worm.

The novel characteristic of my improved gear .is the form of the tooth in longitudinal contour, which is such that the successive teeth are non-parallel and of changing cross-section but which Anevertheless can be generated from a rack of constant pitch. The curve of the tooth. longitudinally is what may be termed a modified involute of a circle and it may be -ofeither two types, respectively designated as extended involutes and abridged involutes. These will -be best understood by reference to the method for generating the same.

As shown in Fig. 1, a is a point on a line b which is rolled without sliding about a circle c and which traces a line d that is a true involute of a circle. If the point a is offset from the line b, either outwardly or inwardly, as indicated at a and a2, such offset points, if maintained in rigid `relation to the me b, will trace modified involute curves d and d2. These are non-parallel with the curve d, but constantly approach the latter and will merge with the same at an infinite distance.

had therein to the accompanyingV Figure 2 shows a series of extended involute curves which are generated by equispaced points e, e etc. on the line f parallel to and outwardly spaced vfrom the line b. Such curves are non-parallel and outwardly divergent and the normals y, g etc. drawn from each curve at the point of intersection with the line f will all intersect in the point iz., which is the point of tangency` of the line b with the base circle c.

Figure 3 shows a series of abridged involute curves which are generated by equispaced points upon the line t' inwardly offset from the .line These curves are also nonparallel and outwardly divergent and moreover the normals drawn from t-he respective curves at the' points of intersection with the line i will all pass through the point ha,

which is the point of tangency of the line b.

If the line f, Figure 2, is regarded as a rack of constant pitch and infinitesimal thickness, this in the movement previously described will generate spiral `teeth of a crown gear, and by reason of the fact that the rack is constantly changing its angular relation to the curves, the teeth generated and also the interdental spaces will be nonparallel, of progressively increasing width and of modified involute curvature.

The peculiar characteristics of these curves is that any series traced by equispaced points-fon the offset line may be arranged tangent to any other series of curves traced by equally spaced points on a line equally-'offset whether the base circles for the two series are the same or different, or whether the offsetting of the line is inward or outward from the base circle, the one generating abridged modified involute curves and the other extended modied involute curves. lVhere the inward offsetting of the line is equal to the radius of the base circle, the curves generated become Archimede'an spirals and may in development form a helix of constant lead on the surface of the cone. Therefore, by 'constructing a conical hob, which in axial section forms a rack of constant pitch, such a hob is capable of generating in the gear blank nonparallel curves of the character described 'and without interference or mutilation.

The method of generating my improved gears forms the subject-matter of another tion is a rack of constant pitchcorresponding to the pitch desired in 'the gears to be generated; second, in'setting the hob ini-ela;

tion to the ear blank Gr so thatthe pitch cones thereo are tangent to a common plane and the axis of the hob is o'set'rom the imaginary base circle of the gearV to be n erated equal tothe radius of itsown ase circle' third; in relatively rotating the hob and the gear blank so that each revolution of the hob will advance one tooth of thev gear if' the hob is of sin 1e thread or a plurality of teeth if of multiple thread; fourth in imparting a movement of translation o the hob about a segment of the base circle vof the gear blank, such movement being suicient to pass completely across lthe face of the blank. as indicated in Fig. 5;

Figure 6 illustratesv la portion of a gear of` my improved construction' in which the teeth are shown to be generated by a rack of constant pitch and Ato have a longitudinal curvature of an extended involute. Figure? is a plan view showinga crown gear B in imesh with a pinion D both of abridged modified involutc curvature. Either Jform' of gear will perfectly mesh with a similargear o-the opposite hand (richt or left),

which is generated by an equahob of the' opposite hand. Also, all gears which are generated by thesame hob and which have the same base circle will mesh with all gears ene-rated by an equal hob of the opposite Eend and which have the same base circle. As diagrammatically illustrated in Fig. 8, my improved gear E can be superposed over a tapering worm F and will mesh with same correctly and without interference, and any ca able of running in mesh with a Worm.`

at l claim as my invention is: l. A bevel gear oa form such as might be generated by rolling a conical blank upon a crown gear, the latter having aseries of teeth which are longitudinally of modified.

. involute curvature and are non-parallel.

2. A bevel gear cfa form such as might be generated by rolling a conical blank upon a crown gear, the latter having a series of teeth which are longitudinally of modified 'in vofluto-l curvature and@ are non-parallel,

said curves in the pitchv plane being generated by vequi-spaced points on aline parallel to. and in rigid relation to a line rolling, withoutsliding'fupona base circle'.

3.v A bevel a'r of a Aform such as might be generated y rolling -aconical blank on a crown gear, the latter having teeth'which' are substantially such as generatedv bythe movement of a rack 01E,- constant pitch in lixedparallel spaced relation to a line rolling upon a base circle concentricwith the axis 'of the crown gear. l

4s -A bevel gear wheel of a lornil. which might be generated byl rolling a vconical blank upon a crown gea-r, having teeth longitudinally .of modified involute outwardly divergent curvature, all of said curves being substantially such as may be traced by points on a line in fixed' spaced parallel 'rclation to a line rolling, without sliding, upon a 'base circle concentric with the anis of the crown gear. i .F.- ,Y

5. A system of mating spiral bevel gears arrangedl with their axes non-intersecting and non-parallel the teeth of, which `in their longitudinal contour are spirals of the gcneral nvolute type having dilerent base radii but the same absolute value of modification with respect to a common involute ci a circle. l i 1 6. A s stem of mating spiral bevel gears having t eir axesxnon--intersecting and nonparallel, the teeth of which may be gener ated bythe movement of a rack of constant libl itch .rolling on the pitchfcoues of conical lanks along a series of geodesic lines.l

7. A system of mating spiral gears, one of which is beveled, saidgears having axes which are non-intersecting and non-parallel and the longitudinal curvature of the teeth of which alrein develo ment respectively' Archimedean spirals'an 'modified involute curves( 8. A system of mating spiral lgears having their axes non-intersecting and nonparallel, one of said gears being a conical screw' which may be developed by a 4rech of constantpitch, while the other is a conjugate wheel' generated by said conical screw when both are brought into a mutual tangential position and rotated in reverse ratio to tl-llieir respective 1`numbers of threads or teet --l'In testimonyqyvhereof I ailix my si ature.

KOLA. TRBOJE IGH. 

